nusdns06.digitalarchives.com has no MX records.
Question and response
Question
dig nusdns06.digitalarchives.com. MX
Answer
The response has no answer records.
Authority
digitalarchives.com. 900 SOA nusdnsgm01.ironmountain.com. webmaster.ironmountain.com. 2005031859 10800 3600 2592000 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0